RTD elements are frequently mounted in a metallic sheath of very small diameter. In the prior art, a typical mode is to locate the device within a sheath, say stainless steel, and to obtain rigidity by surrounding the device with a highly compacted mass of some particulate refractory, say, MgO. One common type of RTD capsule comprises a resistance in the form of a conductor helically wound on an insulating mandrel and the embedment of the winding in a glass or ceramic insulant which, when viscous, fuses with the mandrel. Since numerous applications prescribe the utmost possible accuracy in conversion of temperature to voltage, every precaution is taken to avoid the effects of vibration and shock by immobilizing the element. Prior practice frequently overlooked the possibility of damage resulting from compacting the MgO and careless handling.
The present invention relates to an improved RTD probe and the method of fabricating the same. The improved method disclosed herein decreases the cost and increases reliability, while eliminating problems encountered with prior methods, e.g. wherein an RTD element is joined to two or more conductors carried in the sheath while these latter are exposed for access; in such methods the element and joints are subsequently enclosed by a metal sleeve which is then joined to the metallic sheath of the probe, and a powdered refractory is then packed between the sheath and elements therewithin. The present invention eliminates the problems of these prior practices.